1. Field of Invention
The present invention relates to a method for diffusion treatment of a coating on an engineering part resistant to marine climate.
2. Related Art
With the rapid growth of science and technology, more and more engineering equipment is applied in offshore water and ocean, but its service environment is generally higher than level C5 according to ISO 9225 environmental assessment standard and belongs to extremely harsh environment with rainy, high temperature, salt misty and strong wind. Comprehensive actions of strong atmospheric corrosion, electrochemical corrosion and current scour corrosion on exposed parts cause service lives of various steel structures to be far shorter than that in the common inland outdoor environment. For example, wind power generating device, one of typical engineering devices, services under marine climate, and because wind turbines utilize wind energy to generate electricity, and there is rich wind resources at coast lines and offshore waters, most wind power plants are located at coastal or offshore waters. Wind turbines serviced in marine climate with common protective measures are usually seriously corroded within only a couple of months because the external members, such as engine rooms, engine covers, tower structures, etc., are directly exposed in extremely corrosive atmosphere, which brings about huge losses. According to statistics, the loss caused by marine corrosion accounts for one third of total loss, and the loss of accidents caused by marine corrosion is uncountable. For instance, in 1969 a Japanese 50 thousand ton special ore transport vessel suddenly sank due to corrosion brittle damage. Therefore, it is strategically significant to enhance corrosion control and reduce the loss of metal material to prevent equipment from suffering premature or accidental damage in marine environment.
The rapid growth of modern surface engineering technology provides diverse solutions such as electroplating, chemical plating, thermal spraying, vapor deposition, etc. for corrosion protection on surface of steel. But the above solutions have certain problems, in which the common problems are complex processes and high production cost, and more seriously, a coating obtained by the above methods easily flakes off resulting in failure under the effect of stress and environment. Therefore, it has been an urgent need of current industry development to develop an effective novel process for improving combination strength between a coating and a substrate.